1. Field of the Invention
The present invention relates to a multi-core optical fiber and an optical transmission system.
2. Description of the Related Art
It is foreseeable that the time will come that, along with drastic increase in Internet traffic in recent years, the transmission capacity is short only by a transmission method using only a fundamental mode of an optical fiber for transmission. As a method for solving this, spatial multiplexing technology using a multi-core optical fiber or mode-multiplexing technology using a multi-mode optical fiber is regarded as promising. For example, in Katsunori Imamura, et al., “Effective Space Division Multiplexing by Multi-Core Fibers,” ECOC2010, P1. 09 (2010), optimal designing regarding an SMF-type solid-type multi-core optical fiber is reported. In addition, in Katsunori Imamura, et al., “Multi-core holey fibers for the long-distance (>100 km) ultra large capacity transmission,” OFC/NFOEC 2009, OTuC3(2009), optimal designing regarding a holey-type multi-core optical fiber is reported. Furthermore, in Nobutomo Hanzawa, el al., “Demonstration of mode-division multiplexing transmission over 10 km 2-mode fiber with mode coupler,” OFC/NFOEC2011, OWA4(2011), the result of evaluation for transmission characteristics using a 2-mode optical fiber is reported. On the other hand, it is also considered to be a future important object, along with increase in transmission capacity, to restrain non-linear phenomenon in an optical fiber by enlarging effective core area Aeff of the optical fiber. For example, in Marianne Bigot-Astruc, et al., “125 μm glass diameter single-mode fiber with Aeff of 155 μm2” OFC/NFOEC2011, OTuJ2(2011), an optical fiber of which Aeff is enlarged to 155 μm2 by optimizing refractive index profile by using trench structure is proposed. In addition, In Yoshinori Yamamoto, et al., “OSNR-Enhancing Pure-Silica-Core Fiber with Large Effective Area and Low Attenuation,” OFC/NFOEC2010, OTuI2(2010), an optical fiber of which Aeff is enlarged to 134 μm2 by optimizing refractive index profile by using a W-shaped structure is also proposed.